Diamond enhanced cutting elements, earth-boring tools employing diamond-enhanced cutting elements, and methods of making diamond-enhanced cutting elements

Abstract

Cutting elements for use in earth-boring applications include a substrate, a transition layer, and a working layer. The transition layer and the working layer comprise a continuous matrix phase and a discontinuous diamond phase dispersed throughout the matrix phase. The concentration of diamond in the working layer is higher than in the transition layer. Earth-boring tools include at least one such cutting element. Methods of making cutting elements and earth-boring tools include mixing diamond crystals with matrix particles to form a mixture. The mixture is formulated in such a manner as to cause the diamond crystals to comprise about 50% or more by volume of the solid matter in the mixture. The mixture is sintered to form a working layer of a cutting element that is at least substantially free of polycrystalline diamond material and that includes the diamond crystals dispersed within a continuous matrix phase formed from the matrix particles.

What is claimed is: 
     
       1. A cutting element for use in subterranean drilling applications, comprising:
 a substrate; 
 at least one transition layer bonded to the substrate, the at least one transition layer comprising:
 a continuous first matrix phase; and 
 a discontinuous first diamond phase dispersed throughout the first matrix phase, wherein the first diamond phase occupies a first volume percentage of the at least one transition layer; and 
 
 a working layer bonded to the at least one transition layer on a side thereof opposite the substrate, the working layer comprising:
 a continuous second matrix phase; and 
 a discontinuous second diamond phase dispersed throughout the second matrix phase, wherein the second diamond phase occupies a second volume percentage of the working layer, the second volume percentage is greater than the first volume percentage, and the working layer is at least substantially free of polycrystalline diamond material. 
 
 
     
     
       2. The cutting element of  claim 1 , wherein a difference between the first volume percentage and the second volume percentage is about 50 percentage points or less. 
     
     
       3. The cutting element of  claim 2 , wherein the difference is at least about 25 percentage points. 
     
     
       4. The cutting element of  claim 2 , wherein the first volume percentage is between about 65% and about 85% and the second volume percentage is between about 35% and about 65%. 
     
     
       5. The cutting element of  claim 1 , wherein each of the transition layer and the working layer further comprises another discontinuous hard phase. 
     
     
       6. The cutting element of  claim 5 , wherein the another discontinuous hard phase comprises a carbide material. 
     
     
       7. The cutting element of  claim 1 , wherein the at least one transition layer comprises a first transition layer and a second transition layer, the first transition layer bonded directly to the substrate, the second transition layer being interposed between and bonded directly to the first transition layer and the working layer, the second transition layer comprising more diamond by volume than the first transition layer. 
     
     
       8. The cutting element of  claim 7 , wherein a difference between a volume percentage of diamond in the first transition layer and a volume percentage of diamond in the second transition layer is about 53 percentage points or less. 
     
     
       9. The cutting element of  claim 1 , wherein each of the first matrix phase and the second matrix phase comprises a metal alloy based on at least one of iron, cobalt, and nickel, the metal alloy including at least one melting point reducing constituent, the metal alloy having one of a melting point and a solidus point at about 1200° C. or less. 
     
     
       10. The cutting element of  claim 1 , wherein at least one of the first diamond phase and the second diamond phase comprises a plurality of diamond particles forming a gradient in at least one of particle concentration and average particle size within at least one of the at least one transition layer and the working layer. 
     
     
       11. An earth-boring tool, comprising:
 a body; and 
 at least one cutting element carried by the body, the at least one cutting element comprising:
 a substrate secured to the body; 
 at least one transition layer bonded to the substrate, the at least one transition layer comprising:
 a continuous first matrix phase; and 
 a discontinuous first diamond phase dispersed throughout the first matrix phase, wherein the first diamond phase occupies a first volume percentage of the at least one transition layer and the first diamond phase is at least substantially comprised by isolated single diamond crystals at least substantially surrounded by the first matrix phase; and 
 
 a working layer bonded to the at least one transition layer on a side thereof opposite the substrate, the working layer comprising:
 a continuous second matrix phase; and 
 a discontinuous second diamond phase dispersed throughout the second matrix phase, wherein the second diamond phase occupies a second volume percentage of the working layer, the second volume percentage is greater than the first volume percentage, and the second diamond phase is at least substantially comprised by isolated single diamond crystals at least substantially surrounded by the second matrix phase. 
 
 
 
     
     
       12. The cutting element of  claim 11 , wherein a difference between the first volume percentage and the second volume percentage is about 50 percentage points or less. 
     
     
       13. The cutting element of  claim 12 , wherein the difference is at least about 25 percentage points. 
     
     
       14. The earth-boring tool of  claim 11 , wherein the body comprises a roller cone of an earth-boring rotary drill bit. 
     
     
       15. The earth-boring tool of  claim 14 , wherein the substrate comprises a generally cylindrical body having a dome-shaped end, at least a portion of the generally cylindrical body disposed within a recess in a surface of the roller cone, the at least one transition layer and the working layer of the at least one cutting element disposed on a surface of the dome-shaped end of the generally cylindrical body. 
     
     
       16. A method of fabricating a cutting element for use in subterranean drilling applications, the method comprising:
 mixing a first plurality of discrete diamond crystals with a first plurality of matrix particles comprising a metal matrix material to form a first mixture, wherein the first plurality of discrete diamond crystals occupies a first volume percentage of the first mixture; 
 mixing a second plurality of discrete diamond crystals with a second plurality of matrix particles comprising a metal matrix material to form a second mixture, wherein the second plurality of discrete diamond crystals occupies a second volume percentage of the second mixture, the second volume percentage being greater than the first volume percentage; 
 sintering the first mixture to form a transition layer including the first plurality of discrete diamond crystals dispersed within a continuous first matrix phase formed from the first plurality of matrix particles; 
 sintering the second mixture to form a working layer at least substantially free of polycrystalline diamond material and including the second plurality of discrete diamond crystals dispersed within a continuous second matrix phase formed from the second plurality of matrix particles; 
 bonding the transition layer to a substrate; and 
 bonding the working layer to the transition layer on a side thereof opposite the substrate. 
 
     
     
       17. The method of  claim 16 , wherein bonding the working layer to the transition layer comprises:
 contacting the first mixture adjacent the second mixture; and 
 simultaneously sintering the first mixture to form the transition layer and sintering the second mixture to form the working layer while the first mixture contacts the second mixture. 
 
     
     
       18. The method of  claim 17 , wherein bonding the transition layer to the substrate comprises:
 contacting the first mixture with the substrate; and 
 sintering the first mixture to form the transition layer while the first mixture contacts the substrate. 
 
     
     
       19. The method of  claim 17 , wherein bonding the transition layer to the substrate comprises:
 contacting the first mixture with a substrate precursor mixture; and 
 simultaneously sintering the first mixture to form the transition layer and sintering the substrate precursor mixture to form the substrate while the first mixture contacts the substrate precursor mixture. 
 
     
     
       20. The method of  claim 16 , further comprising at least partially coating the discrete diamond crystals of at least one of the first plurality of discrete diamond crystals and the second plurality of discrete diamond crystals with a coating comprising at least one of W, Ti, Ta, or Si, a carbide of W, Ti, Ta, or Si, and a boride of W, Ti, Ta, or Si.